Glass Melting Technology: A Technical and Economic ... - OSTI

Four test series using oxy-gas burners have been conducted in the pilot-scale submerged
combustion melter. Combustion was stable over a turndown ratio of more than 3:1, and the
burners were easily started, shut down, and restarted as desired. The coarse feeder was used for
all tests. The air-gas burners and the fines feeder have not yet been tested under high-temperature
melting conditions. All tests were conducted in batch mode, feeding known quantities of raw
material into the melt from the coarse feeder and then producing a bubbling melt in the melt
chamber. Sodium silicate, rather than soda ash and silica, was tested to produce a viscous melt.
More than 100 kg of sodium silicate was charged, and a product melt was collected.
Several mineral wool compositions and cement kiln dust were also tested to demonstrate the
wide range of stable operating capabilities of the SCM unit. This intensified the heat exchange
between the products of combustion and the processed material while lowering the average
combustion temperature. The intense mixing of the melt increases the speed of melting,
promotes reactant contact and chemical reaction rates, and improves the homogeneity of the
glass melt product. The melter can also handle a relatively non-homogeneous batch material. The
size, physical structure, and especially the homogeneity of the batch feed do not require strict
control. Batch components can be charged either premixed or separately, continuously or in
portions.
Stable, controlled combustion of the fuel within the melt is critical. Simply supplying a
combustible mixture of fuel and oxidant into the melt at a temperature exceeding the ignition
temperature of the fuel does not sufficiently stabilize combustion. A physical model for the
ignition of a combustible mixture within a melt, as well as its mathematical description, shows
that for the majority of melt ignition of a combustible mixture injected into the melt as a stream
starts at a significant distance from the injection point. This leads to the formation of cold
channels of frozen melt and explosive combustion. To avoid this, GTI has designed several
multiple nozzle burners to minimize the ignition distance in one of three ways: 1) by stabilization
of the flame at the point of injection using special stabilizing devices; 2) by splitting the fueloxidant
mixture into smaller jets; or 3) by preheating the fuel/oxidant mixture.
Commercial SCM applications could be extended from mineral wool to a range of commercial
products including cement, sodium silicate, fiberglass, and waste vitrification. SCM holds strong
promise as the melting step of a glass system, but solutions must be found for the problems of
batch handling, integrated melting and fining, heat recovery, process sensors and control, scaling
up from 75 tpd, and volatilization.
SCM technology has recently been confirmed for use in the production of high-temperature
mineral melts. Five 75tonne/day melters are in operation, two in Ukraine and three in Belarus.
The Gas Institute (GI) of the National Academy of Sciences of Ukraine has developed SCM
technology.
The insulating materials produced to date in the commercial operations in the former Soviet
Union were basalt mineral wool products. The chemistry of this product does not have alkali or
borates. In the extension of this technology to alkali and borate glass compositions, researchers
should anticipate refractory and air emission challenges not previously experienced.
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